Tina Fey and Amy Poehler aren't able to pump many laughs out of Baby Mama.

Opens Friday, April 25, at multiple locations.

Could have sworn I've seen this episode of Baby Mama before — like sometime in January 2007, when it was originally titled "The Baby Show" and aired on the other prime-time series starring Tina Fey, 30 Rock. (Waitaminute — you say Baby Mama's a movie and not a TV show? Seriously? Coulda sworn...) It was funny the first time around when Fey, as late-night-TV exec Liz Lemon, suddenly found herself drawn to the sound of cooing and the scent of baby powder. After a poorly placed phone call to the world's worst fertility/meth-addiction doctor ("I should start by saying that I can't personally help you conceive. Something happened to me while scuba diving"), Liz wound up snatching an adorable tyke from a hairdresser — totally by accident, but still, dark, weird stuff.

Baby Mama extends the joke, then softens it, then smothers it in its crib — an unpleasant picture, but not any more disagreeable than the phrase "Produced by Lorne Michaels." Ultimately, that's all this shrugging disappointment is: a Saturday Night Live sketch stretched a good hour past its breaking point of no return.

Pairing Fey with her former "Weekend Update" co-anchor Amy Poehler, Baby Mama's little more than Tommy Boy on estrogen-replacement therapy — one more wa-a-a-a-cky SNL buddy comedy. Even Fey — who managed to stay sharp as a prison-yard shiv while toiling on Michaels' anesthetizing assembly line — has fallen victim to the boss man's familiar failings as a filmmaker, wherein he plucks the show's famous cast members and asks them only to do more of that. Michaels actually has Fey to thank for his sole solid producing credit: Mean Girls, which Fey wrote and appeared in alongside Poehler, was a knockout, and the exception to the SNL-movie rule — which is why, ultimately, Baby Mama is more disappointment than disaster. But Fey didn't write this one; first-time director Michael McCullers did — he of such duds as Thunderbirds and Undercover Brother, which only felt like a Lorne Michaels production.

Fey's now called Kate Holbrook, and instead of a NBC TV exec, she's a VP at a Whole Foods knockoff called Round Earth. And instead of working for a slicked-back boss played by Alec Baldwin, she's working for a pony-tailed boss played by Steve Martin as a puffy hippie-dippy dope who rewards his execs with things like five minutes' worth of uninterrupted eye contact. (Martin, who says things like "I am a great man, and great men do great things," hasn't been so deadpan or dead-on in ages; he steals the show from the sidelines.)

Kate, of course, wants a baby: She visits a sperm bank, consults doctors, and plasters her apartment with Post-It notes bearing such think-positive aphorisms as "Yes! Be Fertile!" before turning to Poehler's surrogate womb. A single woman who frightens off prospective mates with too-much-information monologues over dinner, Kate is more than content to live the "alternative lifestyle" — that is, be a single mom. But as the Coen Brothers put it in Raising Arizona, her insides are a rocky place where a man's seed can find no purchase — something to do with a T-shaped uterus. She's left with but one choice: a surrogacy firm run by Sigourney Weaver's regal rip-off artist Chaffee Bicknell, who's in her late fifties but still quite capable of cranking out babies — worth mentioning solely because Weaver's age becomes the source of countless jokes that give the film the stale flavor of a Comedy Central roast. (When Weaver says she's "expecting," Poehler mutters: "Expecting what — a Social Security check?" It never gets any funnier.)

Kate outsources her pregnancy for $100,000 and winds up with a "dumb white-trash" couple on her doorstep: Angie Ostrowiski (Poehler) and her husband Carl (Dax Shepard). Poehler doesn't seem sure what to do with Angie, who occasionally speaks in a hillbilly accent unless it disappears altogether and she's just Amy Poehler killing time till the next commercial break. She never commits to the part of a chain-smoking mercenary trolling for embryos to make rent, perhaps because to do so would create too wide a chasm between upper-class Kate and broke-ass Angie and render the film's main story line — the development of a friendship by the 40-minute mark — too unbelievable.

Ultimately, the movie exists solely to reunite a winning comic duo: two women so singularly in sync that, during their stint on "Weekend Update," they genuinely laughed at each other's jokes despite their no doubt well-worn familiarity come showtime. Kate and Angie are just Tina and Amy goofing around — drunk-dancing, crooning along to video-game karaoke, and, once more, finishing each other's sentences. I'd rather watch MILF Island.